The Indo-Pacific lionfishes Pterois miles and P. volitans (in the scorpionfish family, Scorpaenidae) were at one time not distinguished from each other, but today they are widely recognized as distinct species based on morphometric and mitochondrial DNA analyses (Hamner et al. 2007; Betancur-R. et al. 2011; Eschmeyer 2012). Both of these predatory, venomous species have achieved notoriety during the past decade as they have invaded the western Atlantic with extraordinary speed, raising major concerns about their impacts on native hard-bottom, mangrove, seagrass, and coral reef communities. In a study in the Bahamas (Green et al. 2012), lionfish abundance was found to have increased rapidly between 2004 and 2010, by which time lionfish accounted for nearly 40% of the total predator biomass in the system. This increase in lionfish abundance coincided with a rapid (over just two years) 65% decline in the biomass of the 42 Atlantic fishes recorded as lionfish prey. These lionfishes have now been far more thoroughly studied in the western Atlantic than in their native range.

The lionfish invasion has spread all along the coastal Yucatan Peninsula, including the entire Mesoamerican coral reef, and throughout the Caribbean as far as Venezuela. (Valdez-Moreno et al. 2012). Lionfish were first recorded in the western Atlantic in 2000. They have been established from Miami to North Carolina (U.S.A.) since 2002, around the Greater Antilles since 2007, and around the Florida Keys and Gulf of Mexico since 2009. Lionfish were numerous around Bermuda by 2004 and established in the Bahamas by 2005. Since 2009, lionfish have extended their range to include the Caribbean coasts of Mexico and Central and South America to Venezuela. It is unclear whether they will be able to spread south of Brazil or Uruguay. Juveniles can be found as far north as Rhode Island (U.S.A.), but under current climate conditions they apparently cannot withstand winter temperatures north of North Carolina. Lionfishes are the first nonnative marine fishes to establish in the western North Atlantic and Caribbean, although at one time or another dozens of of non-native marine fishes (most from the Indo-Pacific) have been documented in the coastal waters off Florida. (Schofield 2010) The native range for P. volitans is the Indo-West Pacific: Christmas and Cocos-Keeling islands (Indian Ocean)and the western Pacific to the Line Islands, French Polynesia, and Australia to Japan. The native range for P. miles is in the Red Sea and Indian Ocean: East and South Africa, Madagascar and the Mascarenes east to Indonesia; this species has reached the Mediterranean Sea from the Red Sea through the Suez Canal (Eschmeyer 2012)

The establishment of lionfish in the western Atlantic is believed to be the result of accidental or intentional releases from aquaria. Genetic analyses have revealed a striking reduction in genetic diversity in introduced populations relative to their native ranges (Hamner et al. 2007; Betancur-R. et al. 2011), but this has not caused any obvious problems for these new populations, which reach densities far higher than do populations in their native range (Kulbicki et al. 2012). Mitochondrial DNA screening of western Atlantic lionfish has shown that while P. miles is restricted to the northernmost locations (Bermuda and the US east coast), P. volitans is ubiquitous and much more abundant (Betancur-R. et al. 2011). Discouragingly, modeling by Barbour et al. (2011) suggests that effective lionfish removal programs would be very difficult to implement and maintain.

The venom-packing spines of lionfish pose a danger to anyone handling them.

Albins and Lyons (2012) reported a previously undescribed technique used by P. volitans to capture fish prey. While slowly approaching prey, lionfish produce jets of water directed toward their prey. These jets may confuse or distract prey and often result in prey fish facing the attacking lionfish, increasing the probability of head-first capture and swallowing.